Steam turbines power plants typically utilize a trip throttle valve to control the introduction of high pressure steam to the steam turbine. The trip throttle valve may be electrically coupled to a control system capable of monitoring certain conditions indicative of imminent danger to the steam turbine, e.g., rotor overspeed. When such conditions are met, the control system may send a signal to trip the steam turbine, thereby closing the trip throttle valve and preventing the inflow of the high pressure steam to the steam turbine. In order to ensure that the trip throttle valve is in proper working condition, testing of the trip throttle valve should be carried out on a regular basis. Infrequent testing of the trip throttle valve may result in the accumulation of scale or rust that may affect the ability of the trip throttle valve to properly close after receiving the signal to trip. Accordingly, such a malfunction of the throttle trip valve may result in the inability to safely shutdown the steam turbine in the event of a trip condition.
Traditionally, in order to test the trip throttle valve, the steam turbine is tripped, and thus, taken offline resulting in production and economic losses. Accordingly, such drawbacks have led to methods of testing the trip throttle valve without taking the steam turbine offline. For example, one such method includes utilizing a lockout device to isolate trip components of the trip throttle valve to test the trip components without tripping the steam turbine. However, such a practice may leave the steam turbine unprotected from a potential trip condition arising during testing.
What is needed, therefore, is a trip throttle valve which may be tested during operation of the steam turbine while providing for the safe shutdown of the steam turbine in the event of an occurrence of a trip condition during testing.